Two technologies dominate advanced solar module diagnostics: infrared thermography and electroluminescence (EL) imaging. They are often framed as competitors, but they answer different questions and are most powerful when used together. Knowing which to use, and when, saves money and produces better diagnostic outcomes.
What Each Method Actually Does
Thermography images heat. Under load and sunlight, defective cells dissipate energy as heat, and an infrared camera captures the resulting thermal anomalies. It works outdoors, in daylight, at scale, and from a drone — making it the standard for field inspection of operating plants.
Electroluminescence works in reverse. A current is injected into the module in darkness, causing healthy silicon to emit faint near-infrared light. A specialized camera captures this glow; cracked or inactive cell regions appear dark. EL reveals microcracks and cell-level defects with far higher detail than thermography — but it generally requires darkness and direct electrical connection.
The key distinction: Thermography finds defects that are already affecting performance (they're hot because they're failing). EL finds defects that will affect performance — microcracks that haven't yet caused measurable current mismatch. Thermography is the screening tool; EL is the diagnostic microscope.
Side-by-Side Comparison
| Factor | Thermography | Electroluminescence |
|---|---|---|
| What it detects | Active thermal anomalies (hotspots, diode faults, PID) | Microcracks, cell fractures, inactive areas |
| Conditions | Daylight, under load, ≥600 W/m² | Darkness, current injection |
| Speed & scale | Fast, aerial, whole-plant | Slow, module-by-module |
| Field vs. lab | Ideal for field at scale | Best in lab or controlled field setup |
| Standard | IEC 62446-3 | IEC TS 60904-13 |
When to Use Which
Use thermography for routine O&M surveys, annual inspections, post-event screening, and any whole-plant assessment. It's fast, scalable, and catches the defects that are actively costing generation. For when these inspections are warranted, see when solar thermography makes sense.
Use EL imaging when you need to investigate a specific module in depth — for example, to document hail microcracks for a warranty claim, or to characterize a module type showing early failures. EL confirms what thermography flags.
The Combined Workflow
Best practice at scale is sequential: thermography screens the whole plant and identifies anomalous modules; EL then examines the worst cases at cell-level detail. This mirrors the broader two-stage approach described in drone vs. handheld inspection — fast wide-area capture first, detailed investigation second. For field inspection of operating solar assets, thermography remains the primary, most cost-effective method — and the analysis of that thermal data is exactly what we deliver remotely.